WordPress two-factor login plugin bug, er, bypasses 2-factor login

The maker of a popular plugin that provides two-factor authentication for WordPress bloggers is preparing an update – after finding a vulnerability in its system. It advises that anyone using two-factor plugins from any vendor need to check their security strength.

Duo Security's duo_wordpress plugin is vulnerable in some multisite deployments, the company says, allowing someone logged into one site to access a second site in a deployment without going through two-factor authentication.

The problem only exists for those administering multiple WordPress sites, but has implemented duo_wordpress individually on each site, the company says. If the plugin is enabled globally across the sites, there's no problem.

However, Duo Security notes: “We’ve determined that authentication plugins from other two-factor vendors are similarly affected by this vulnerability”, and advises all two-factor users to see if they're vulnerable.

In its customer advisory, here, Duo Security gives the following example:

“A multisite WordPress deployment has two sites, Site1 and Site2, with the Duo WordPress plugin enabled for Site1 but disabled for Site2. Under normal circumstances, users logging into Site1 will be prompted for primary credentials and second-factor authentication; Site2 users will be prompted only for primary credentials. A Site1 user may force-browse to the login URL of Site2, which will authenticate the user (as part of the same Wordpress multisite network), and redirect them back to Site1, without prompting for second-factor authentication.”

Instead of switching two-factor authentication off globally, and on for individual sites, Duo Security advises its users to enable two-factor authentication on a global basis, and then switch it off on an individual basis for roles that don't require it. ®